The goal of the proposed project is to characterize the patterns of neuronal activity in the hippocampus during acquisition and performance of a spatial memory task in rats. Unit and slow-wave activity from multiple hippocampal neurons will be recorded as rats learn and execute a discrete trials alternation task in a T-maze. It is predicted that differential firing patterns accompanying traversal of the stem of the maze will not be apparent during initial training, but will develop as the alternation rule is learned and will predict the animals' eventual turning choice. Additionally, it is predicted that on early trials trial-selective firing will coincide with the positive phase of hippocampal theta activity, the phase that is thought to favor encoding and that on later trials (after the animal has learned the task), the selective firing will occur on the trough of theta, the phase that is thought to favor retrieval. Finally, the information encoded by hippocampal neurons during execution of the alternation task will be further delineated by examining whether patterns of hippocampal activity reflect past or future behavior and by examining the role that ensemble activity that is present between trials plays in subsequent behavior. The results of the proposed study will add to the understanding of the mechanisms of hippocampal involvement in memory and thus could lead to improvements in the treatment of memory disorders such as Alzheimer's disease. [unreadable] [unreadable]